Related Party Transactions (Subcontracting Arrangements) (Narrative) (Details) - Related Contractor Or Supplier [Member] - Management [Member] $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($) employee	Dec. 31, 2016 USD ($)
Subcontracting Arrangements [Member]
Related Party Transaction [Line Items]
Number of additional management employees, subcontracting arrangement | employee	2
Expenses, related party	$ 78.0	$ 12.9
Payables, related party	$ 2.0	0.1
Equipment [Member]
Related Party Transaction [Line Items]
Proceeds from sale of equipment, related party		$ 0.3